Double Colorless Energy provides [C][C]. It provides two Energy both for being able to use attacks and for calculating damage via Aera Ball and other attacks that operate similarly. So if your Lugia-EX has only a Double Colorless Energy attached to it, Aero Ball will hit for a minimum of 40, plus 20 more for each Energy attached to yor opponent's Active Pokemon. If both Active Pokemon have only a DCE attached, Aero Ball does 80. Double Dragon Energy would work the same way, so long as it is attached to a Dragon Pokemon.